1. Field of the Invention
The present invention relates to a body water amount condition judging apparatus for judging condition concerning the amount of body water in a living body by measuring bioelectric impedance using a multi-frequency alternating current.
2. Prior Art
Edema is a kind of morbidity, in which interstitial fluid and/or lymph accumulates at intra-cellular or extra-cellular portions and the amount of water in a body increases. Appearing edema everywhere in a whole body may be realized as a symptom of diseases such as heart disease, kidney disease, liver disease, and such like. Therefore, it is desirable that the degree of edema is measured exactly and it is utilized in diagnosing or in monitoring patients"" condition.
On the other hand, dehydration is a kind of morbidity, in which water in a living body is abnormally reduced, and it often occurs in daily life when a person is exercising or when the temperature is high because a lot of water is excreted from the body by sweating and an elevated body temperature. Especially, it is said that elderly persons are apt to experience dehydration symptoms. This is because, when one becomes older, size of muscles which contain water decreases, the amount of urine increases because the function of the kidneys deteriorates, and awareness of thirsty decreases because the senses are dulled. Another reason is that the amount of water which cells require decreases.
If dehydration symptoms are left untreated, the dehydration symptoms will gradually become worse until a serious dehydration condition is occurring. Usually, it is said that, when one third of the water in a living body is lost, the body temperature regulation is disturbed. This causes the body temperature to increase, and then water in the living body is further reduced. In other words, vicious circle is created, until at last, a heat illness occurs. A heat illness includes conditions such as heat cramp, desert syndrome and heatstroke. Sometimes all the organs in the body are affected by the heat illness. Thus it is desired that dehydration symptoms be detected exactly to avoid the risk of a heat illness.
Japanese Patent Laid-Open Publication No. Hei 11-318845 discloses an apparatus for measuring the total amount of water in a body, thus allowing edema and dehydration symptoms which a person is not aware of to be detected. This apparatus determines the total amount of body water in a living body of a subject easily by measuring a bioelectrical impedance value, thereby allowing the subject to judge his own body water condition, such as edema or dehydration symptoms, based on this measured amount of body water.
It is known that a bioelectrical impedance value changes when the body temperature changes. That is, the bioelectrical impedance value decreases when the body temperature goes up, and the bioelectrical impedance value increases when the body temperature goes down. However, said conventional apparatus, calculating the total amount of body water based on the bioelectrical impedance value, does not take into consideration this fact that the bioelectrical impedance value changes when the body temperature changes. Thus, said apparatus can not determine the total amount of body water precisely, resulting in it being unable to detect the dehydration condition precisely. For example, in a case where the total amount of body water is decreased and the body temperature is raised, and thus a dehydration condition should be detected, the bioelectrical impedance value increases when the total amount of body water is decreased, while on the other hand, the bioelectrical impedance value decreases because body temperature is raised. Thus, when the bioelectrical impedance value is measured, and then the total amount of body water is calculated based on the bioelectrical impedance value to be able to determine whether a dehydration condition has occurred or not based on this calculated total amount of body water, the dehydration condition may not be detected.
In addition, the said apparatus measures only the total amount of body water, and does not judge the body water amount condition taking each component constituting the body water, such as each amount of intra-cellular or extra-cellular fluid, into account. Therefore, the said apparatus can not judge exact and detailed body water condition.
As the said apparatus demands personal parameters of a subject, such as height, age, sex, body weight and the like, to calculate the total amount of body water based on the measured bioelectrical impedance value, the subject has to input such personal parameters into the apparatus. Thus, it is very troublesome for the subjects, especially for elderly subjects, to operate the apparatus. It is desirable for the elderly persons to be measured their total body water frequently, because it is said that elderly persons are apt to experience dehydration symptoms as described above. However, there has been a problem that the elderly persons can not obtain their total amount of body water or obtain them based on wrongly input personal parameters.
Considering the above, an object of the present invention is to provide a body water amount condition judging apparatus which is capable of judging body water amount condition in detail, such as edema condition and/or dehydration condition exactly and easily.
The present invention provides an apparatus for judging body water amount condition, in which at least two values selected from intra-cellular water resistance, extra-cellular water resistance, combined resistance of the intra-cellular and extra-cellular water resistance, and a ratio of intra-cellular and extra-cellular water are judging parameters for body water amount condition, comprises: a multi-frequency bioelectric impedance measuring device; a calculating device; a reference value determining unit; a body water amount condition judging unit; and a display device. Said multi-frequency bioelectric impedance measuring device supplies a plurality of alternating current of different frequencies to a body of a subject and measures a bioelectric impedance value, said calculating device calculates the values of each judging parameter based on the bioelectric impedance value measured, said reference value determining unit determines reference values of the same kind based on judging parameter values calculated prior to each judging parameter of the same kind calculated in the past, said body water amount condition judging unit judges body water amount condition by comparing each calculated judging parameter value with the determined judging parameters of the kind, and said display device displays the judging result of said body water amount condition so judged.
In accordance with the preferred embodiment of the present invention, said calculating device may further calculate at least one of the values of intra-cellular water content, extra-cellular water content and total body water content.
In accordance with one embodiment of the invention, said reference value determining unit may determine that an average value of each judging parameter of the past is a reference value of a judging parameter of the same kind.
In accordance with another embodiment of the invention, said reference value determining unit may further determine that the latest value in judging parameters of the past is a reference value of a judging parameter of the same kind.
In accordance with another embodiment of the invention, said reference value determining unit may determine a reference value of a judging parameter every time the judging parameter is calculated.
In accordance with another embodiment of the invention, said reference value determining unit does not use a value of a judging parameter for determining a reference value of the judging parameter, when the value of the judging parameter is abnormal.
In accordance with another embodiment of the invention, said reference value determining unit may determine that a value of a judging parameter is abnormal, when the difference between each value of the judging parameter and a reference value of the judging parameter of the same kind which is already determined exceeds the predetermined value.
In accordance with another embodiment of the invention, said reference value determining unit determines whether a value of a judging parameter is abnormal or not depending upon the time a bioelectric impedance value is determined for calculating the value of the judging parameter. In accordance with another embodiment of the invention, said apparatus further comprises an abnormal value selecting device, said abnormal value selecting device decides whether a subject uses a value of a judging parameter for determining a reference value or not, and said reference value determining unit determines whether the value of the judging parameter is abnormal or not responding to said abnormal value selecting device.
In accordance with yet another embodiment of the invention, said reference value determining unit decides that a value of a judging parameter is abnormal if the time a bioelectric impedance value is determined for calculating the value of the judging parameter is in the hour of rising for the subject.